This application claims priority on European Patent Application No. 01119852.0, filed Aug. 16, 2001, the entire contest of which are hereby incorporated herein by reference.
The invention generally relates to a power station installation and a method of operating a power station installation.
Steam power installations are known in which a steam turbine is usually employed in a power station installation for driving a generator or, in an industrial installation, for driving a machine. For this purpose, hot and pressurized steam, which acts as the flow medium and which expands in the steam turbine so as to do work, is supplied to the steam turbine. After its expansion, the steam usually reaches a condenser connected downstream of the steam turbine and condenses there. The condensate is then supplied as feed water to a steam generator and, after its evaporation, again reaches the steam turbine so that there is, in general, a closed water/steam circuit. An installation having the components necessary for this purpose and therefore having, in particular, a steam turbine and a steam generator, is also designated as steam turbines or steam power installation.
Likewise known are power station concepts in which a gas turbine process is combined with a steam turbine process in a joint installation. In a gas turbine and steam turbine process of this type, a waste-heat steam generator is connected downstream of the exhaust gas end of the gas turbine, with the exhaust gas from the gas turbine being used to evaporate water in the waste-heat steam generator. The steam generated in the waste-heat steam generator, utilizing the waste heat from the exhaust gas of the gas turbine, is utilized in a steam turbine installation connected downstream of the waste-heat steam generator, which steam turbine installation generally has a plurality of steam turbines. Such a process has substantial advantages in comparison with the pure gas turbine process. The main advantages are the high efficiency and an increase in power. Efficiencies of up to between 56 and 58% are achieved in modern gas/steam installations.
Both a steam power installation and a gas/steam installation, however, require a substantial quantity of fresh water, or at least desalinated sea water, for the steam generation. For this reason, the operation of the steam power installation or a gas turbine and steam turbine installation presents a problem in countries with a small supply of fresh water, for example in the dry desert countries of Africa. Because of the fresh water requirement of the conventional power station concepts based on steam, therefore, only the pure gas turbine power stations are, as a rule, employed in such regions of the earth. The efficiency of a gas turbine power station is, however, distinctly less than the efficiency of a combined power station or a conventional steam power station.
An object of an embodiment of the invention is, therefore, to provide a power station installation which permits operation of a gas turbine with improved efficiency. A further object of an embodiment of the invention is to provide a method of operating a power station installation.
A power station installation is achieved, according to an embodiment of the invention, by a gas turbine and air turbine installation, having a gas turbine to which, downstream of its exhaust gas end, the primary side of a heat exchanger for heating air is connected, which heat exchanger has an air turbine connected downstream of its secondary side.
A completely new installation concept is used whichxe2x80x94in contrast to the conventional combined power stations having a steam process associated with a gas turbine process for examplexe2x80x94permits the utilization of the waste heat in the exhaust gas of the gas turbine, but without involving a steam process. In order to increase the efficiency of a gas turbine installation, the waste heat from the exhaust gas of the gas turbine is, in this case, utilized in a completely novel combined process, namely in a gas turbine and air turbine process. Because fresh water is dispensed with, the gas turbine and air turbine installation of the invention can be employed, particularly advantageously, in regions of the earth where fresh water is only available to a limited extent or can only be obtained at substantial cost.
A particular advantage of this arrangement is that existing gas turbine power stations can be retrofitted, to form a gas turbine and air turbine installation, at a cost which can be appraised. The efficiency advantage, as compared with a pure gas turbine installation, may very rapidly outweigh the investment costs of such a retrofit measure. From initial estimations, the efficiency of the gas turbine and air turbine installation is increased by some 9 to 10 percentage points. The power of such a combined installation, based on a gas and air process, is increased by up to 24% relative to a pure gas turbine process.
Compared with a conventional gas turbine and steam turbine installation, furthermore, there is a markedly reduced requirement with respect to production costs in the case of the gas turbine and air turbine installation according to an embodiment of the invention. This is because essentially lower-cost installation components, such as the heat exchanger and the air turbine, are employed. Compared with this, a steam generator, for example, with a water/steam circuit and the steam turbines downstream, is substantially more expensive in the case of a gas/steam installation and this is so precisely with respect to the material costs.
Depending on the gas turbine type selected, an efficiency of some 45 to 50% can be achieved in the case of the gas turbine and air turbine installation. This installation concept, based on a gas and air process, therefore appears to be particularly interesting in countries which are short of water. The waste heat from the exhaust gas of the gas turbine is used in the heat exchanger, which is connected downstream of the exhaust gas end of the gas turbine, in order to heat air which is supplied to the secondary side of the heat exchanger. The air heated in this way is supplied to the air turbine, which is connected downstream of the heat exchanger and which expands so as to do work.
In a preferred embodiment, an air compressor, which is connected upstream of the secondary side of the heat exchanger, is provided so that compressed air can be supplied to the heat exchanger for heating. In this arrangement, the air is compressed in the air compressor from 1 bar to some 5 to 6 bar. The air compressed in this way is supplied to the heat exchanger so that the compressed air is heated. The employment of an air compressor makes it possible to appropriately increase the pressure condition and temperature condition of the working medium to be supplied to the air turbine, i.e. the compressed and heated air. By this means, more energy is available to the air driving the air turbine, which energy is released to do work on the air turbine for the generation of electricity.
The primary side of a further heat exchanger for heating air is preferably connected downstream of the exhaust gas end of the heat exchanger. Multiple utilization of the waste heat of the exhaust gas flowing out of the gas turbine is possible in this way. A part of the waste heat is first used in the heat exchanger to heat the working medium for the air turbine, i.e. the air. In a second, downstream heat exchanger process, a further part of the waste heat is extracted from the exhaust gas in the further heat exchanger and transferred to air. In analogy with a waste-heat steam generator, it is possible to realize a xe2x80x9cwaste-heat air generatorxe2x80x9d by means of this multistage process, in which processxe2x80x94depending on the pressure and temperature condition of the air heated in a waste-heat/air heat exchanger stagexe2x80x94an air turbine can be employed which is specially adapted to the conditions. A multi-stage operation also provides the particular advantage that the output power of the gas turbine and air turbine installation can be adapted, in a simple manner, to the respectively demanded energy requirement, i.e. a high availability.
The air turbine is preferably connected at its exhaust air end to the further heat exchanger. The exhaust air from the air turbine still has a certain heat content, which can be used in a heat exchanger process. The exhaust air, which has been partially expanded and partially cooled in the air turbine, is supplied, in this arrangement, to the further heat exchanger on its primary side so that, on the secondary side of the further heat exchanger, the waste heat can be transferred to a medium, for example a further working medium, such as air at a lower temperature level. Partially cooled exhaust gas from the gas turbine and, at the same time, partially expanded and partially cooled air from the air turbine can therefore be supplied to the primary side of the further heat exchanger.
In this combination, the waste heat from the exhaust gas of the gas turbine and the exhaust air from the air turbine can be used in a particularly advantageous manner. In this arrangement, the exhaust air flow and the exhaust gas flow can be supplied separately, i.e. in separate primary-side main systems, to the further heat exchanger. Alternatively, it can be supplied jointly as an exhaust gas/exhaust air mixture. In the latter case, a mixing location is provided at which the already partially cooled exhaust gas flow is brought together with the exhaust air flow from the air turbine.
The heat exchanger process then takes place downstream of the mixing location in the further heat exchanger, it being possible for the exhaust gas/exhaust air mixture to release heat to a medium, for example air, which is guided on the secondary side of the further heat exchanger. The medium, for example air, guided on the secondary side of the further heat exchanger is correspondingly heated and is available to the gas turbine and air turbine process for the generation of energy.
In a preferred embodiment, the utilization of the heat available in the further heat exchanger can take place by an air compressor being connected upstream of the secondary side of the further heat exchanger, so that compressed air can be supplied to the further heat exchanger for heating. The compression in an air compressor permits higher pressure and temperature conditions to be achieved in the air heated in the further heat exchanger, which is particularly favorable for the further employment of the air, which has been heated and compressed in this way, in the gas turbine and air turbine process. In this arrangement, the air compressor used for this purpose can be different from the air compressor which is connected upstream of the secondary side of the heat exchanger. It is also possible for the air compressors connected upstream of the secondary side of the heat exchanger and the further heat exchanger to be one and the same air compressor, in which case a partial flow of the air compressed in the compressor is respectively supplied to the secondary side of the heat exchanger and the further heat exchanger. It is also possible for compressed air of different pressure conditions to be supplied to the heat exchanger and the further heat exchanger by a respective tapping at a pressure stage of the single air compressor. A flexible adaptation of the installation concept can be undertaken in this case, depending on the availability of an air compressor or the demand on the gas turbine and air turbine installation with respect to efficiency and power. The compressed air, which is extracted from the further air compressor or, if appropriate, from a second pressure stage of the same air compressor, has a pressure condition of, typically, approximately 2 to 2.5 bar.
In a particularly preferred embodiment, a further air turbine is connected downstream of the secondary side of the further heat exchanger. In this way, the waste heat from the exhaust air or the exhaust gas, which is available in the further heat exchanger, can be utilized in a particularly advantageous manner. For this purpose, heat from the exhaust gas or the exhaust gas/exhaust air mixture is transferred in the further heat exchanger to the compressed air guided on the secondary side and the compressed air, which is heated in this way by heat exchange, is available for expansion, so as to do work in the further air turbine. The overall efficiency of the gas turbine and air turbine installation can therefore be further increased by the provision of second air turbines, at least. Each of the air turbines is then associated with a heat exchanger or a heat exchanger stage, so that a multi-stage operation of the gas turbine and air turbine installation can be achieved with particularly effective utilization of the waste heat available from the gas turbine.
The gas turbine and air turbine installation preferably has a generator for converting mechanical energy into electrical energy.
An object directed toward a method of operating a power station installation can be achieved, according to an embodiment of the invention, by a method of operating a power station installation, in particular a gas turbine and air turbine installation according to the above implementations, having a gas turbine in which the waste heat in the exhaust gas of the gas turbine is used to do work to drive an air turbine.
In this arrangement, waste heat in the exhaust gas of a gas turbine is preferably brought into heat exchange with air, air being heated in the heat exchanger and heated air being supplied to the air turbine.
Also preferred is an arrangement in which the air is heated by heat exchange with the exhaust gas and/or with an exhaust gas/exhaust air mixture.
In a further preferred embodiment of the method, the air is compressed and, in particular, the air is compressed before a heat exchange process, so that compressed and heated air can be employed for expansion, so as to do work, in the air turbine.
The advantages of the method occur in an analogous manner to the advantages of the gas turbine and air turbine installation described further above.